Describe the role of genes in protein synthesis.

Genes play a crucial role in protein synthesis, which is the process by which cells create proteins. These proteins are essential for almost every function in the cell, including catalyzing biochemical reactions, providing structure, and regulating processes. The process of protein synthesis can be broken down into two major stages: transcription and translation.

1. Transcription (DNA to mRNA)

Transcription is the first step in protein synthesis, where the information encoded in a gene (DNA) is copied into a messenger RNA (mRNA) molecule. Here’s how genes are involved in transcription:

  • Gene Activation: When a specific protein or signal activates a gene, the DNA double helix in that region unwinds.
  • RNA Polymerase: An enzyme called RNA polymerase binds to a specific region of the gene, known as the promoter. This marks the start of transcription.
  • RNA Synthesis: RNA polymerase moves along the DNA strand, reading one of the DNA strands (the template strand) and synthesizing a complementary strand of mRNA. This mRNA is a copy of the gene’s coding sequence, except that uracil (U) replaces thymine (T) in RNA.
  • Splicing: In eukaryotic cells, the newly formed mRNA (called pre-mRNA) undergoes splicing, where introns (non-coding regions) are removed, and exons (coding regions) are joined together to form the mature mRNA.
  • Transport: Once the mRNA is processed, it leaves the nucleus and enters the cytoplasm, where translation occurs.

Gene’s Role: The gene provides the specific sequence of DNA that is transcribed into mRNA. This sequence will later determine the amino acid sequence of the protein produced.

2. Translation (mRNA to Protein)

Translation is the process where the information carried by mRNA is used to assemble a protein. It takes place in the ribosomes, which are located in the cytoplasm (or on the rough endoplasmic reticulum in eukaryotic cells). Here’s how genes play a role in translation:

  • mRNA Binding: The mature mRNA binds to a ribosome, which consists of ribosomal RNA (rRNA) and proteins. The ribosome reads the mRNA in sets of three nucleotides called codons. Each codon specifies a particular amino acid.

  • Transfer RNA (tRNA): The tRNA molecules act as “adapters” that carry specific amino acids to the ribosome. Each tRNA has an anticodon region that pairs with a complementary codon on the mRNA.

  • Amino Acid Assembly: As the ribosome moves along the mRNA, the tRNA molecules bind to the corresponding codons. The ribosome catalyzes the formation of peptide bonds between the amino acids carried by the tRNA. This results in the synthesis of a polypeptide chain (a sequence of amino acids).

  • Protein Folding: Once the polypeptide chain is fully synthesized, it undergoes folding into a specific three-dimensional structure to form a functional protein. The final structure is essential for the protein’s activity.

Gene’s Role: The sequence of codons in the mRNA, which is directly determined by the sequence of nucleotides in the gene, dictates the order of amino acids in the protein. This sequence ultimately defines the structure and function of the protein.

Key Points in Protein Synthesis:

  • Genes encode the information for proteins in their DNA sequence.
  • Transcription is the process where the gene’s DNA sequence is copied into mRNA.
  • mRNA carries the genetic information from the nucleus to the ribosomes in the cytoplasm.
  • Translation is the process by which the ribosome reads the mRNA and assembles amino acids into a polypeptide chain, which then folds into a protein.

3. Regulation of Protein Synthesis

The synthesis of proteins from genes is tightly regulated. Not all genes are expressed at all times or in all cells. Gene expression is influenced by various factors, including:

  • Promoters: Regulatory sequences in the gene that control when and how often the gene is transcribed.
  • Enhancers and silencers: Sequences that can increase or decrease the expression of a gene, respectively.
  • Transcription factors: Proteins that bind to DNA and help or prevent RNA polymerase from transcribing a gene.
  • RNA processing and degradation: The mRNA can be modified or degraded in the cytoplasm, affecting how much protein is produced.

Related Questions:

  1. How do genes control inheritance of characters?
  2. Explain the composition of chromatin material.
  3. Give an account of genes and alleles.
  4. Write the differences between:
  5. Name sources of variation.
  6. Give examples of artificial selection.
  7. What kind of gametes would be produced by organisms having the following genotypes?
  8. Two white sheep produce a black offspring. What must the parents’ genotype for colour be? What is the probability that the next offspring will be black?
  9. The diagram shows two varieties of moths in England.
  10. Among the following genotypes, which ones are heterozygous and which are homozygous? Which of the genotypes have the same phenotype?
  11. Describe the role of a gene in protein synthesis.
  12. State that nitrogen is important in protein synthesis and magnesium for chlorophyll formation.
  13. Name the structure through which the exchange of gases can take place in plants.
  14. Name the ways through which a plant can obtain oxygen.
  15. Why should one not sleep under a tree at night?
  16. Why would very wet soil be dangerous to plants
  17. Why do plants not need a specialized respiratory system?
  18. How does the exchange of gases take place in alveoli?
  19. What is the effect of exercise on the rate of breathing?
  20. Compare inspired air and expired air.